When you have a child in your custody but also have a parenting plan you're supposed to follow, the last thing the court wants to see is your refusing visitation to the other parent. Unless there are extreme circumstances, like situations involving abuse, there is no reason you should violate a court order.
Things happen, and there may be a day or two where you can't follow through on a visit with the other parent because of work or other events. The same might be true for him or her. When it comes to a normal day, though, it's not okay to prevent your child from seeing the other parent.
Parental alienation is considered to be a form of domestic abuse.
Another thing you need to prevent is the alienation of a parent simply due to your own actions. For instance, it is not fair to tell your child how horrible your ex-husband is while also suggesting that your child stays away from him or her. This starts a horrible process of parental alienation that is neither fair nor acceptable to the court.
You could be accused of Malicious Mother Syndrome.
Despite being called Malicious Mother Syndrome, this can affect men or women. It's a misnomer, but it describes a situation where one parent tries to prevent the other access to their child. The parent may also try to punish the divorcing parent by alienating the children from them or lying to the children about their parent.
People with this syndrome have no other mental health concerns that can account for the actions they're taking. Additionally, this is not actually a recognized medical condition but is enough to cause a judge to consider restricting your own rights as a parent and reinforcing the other parent's access to your children.
Sometimes, there's a good reason to prevent visitation. In those cases, it's important to talk to your attorney and to seek a change in the custody plan. Until then, unless it is an emergency, you should continue to follow your court-ordered visitation schedule.